Motorists are set to claim back millions of pounds in fines after it emerged a speed camera has been illegally catching them for 10 years due to an administrative blunder.

More than 50,000 drivers have been wrongly flashed by the Gatso device because the road used to mark out a 30mph zone doesn't exist.

The error was spotted by an eagle-eyed judge during the case of a lorry driver who was filmed travelling at 11mph over the limit on the A35 at Chideock, Dorset.

According to the official Highways Agency paperwork, the length of the speed restricted zone is measured from the junction of "Seatown Road" in the village.

But judge Anne Arnold realised that although locals refer to the side road off the A35 as Seatown Road, there is no such place on any map.

The court heard that the road is actually called Duck Street. Locally it is known as Seatown Road because it leads to the coastal village of Seatown.

As a result, the court ruled that Mr Dawe's speeding ticket invalid and as a consequence every fine dished out using the camera might also be null and void.

Every motorist who has been caught by the camera is now being urged to claim back their fines - worth more than three million pounds.

Mr Dawe, 52, from St Austell, Cornwall, said: "The money that camera has raked in has effectively been stolen because that speed restriction is not legal.

"I have already written to Dorset police asking for the names and addresses of every motorist who has been flashed by that camera because I feel I have a moral obligation to make sure they get their money back.

"As my barrister said afterwards, this could be one of the costliest mistakes of its kind in Britain because it has been going on for so long.

"I am sure most drivers who have received a fine in the post would have paid up without thinking twice about it.

"But they should now write to the police or the courts and demand their money back and the points wiped off their licence."

The blunder occurred when the Highways Agency issued a road restriction notice under the Road Traffic Act 1984 for a stretch of the A35 on the approach to Chideock, near Bridport, in 1997.

Part of the order states: "To impose a 30mph speed limit on the A35 at Chideock, between a point 630 metres east of its junction with Seatown Road and a point 810 metres east of that junction, a total distance of approximately 180 metres."

Mr Dawe was driving from Southampton to Cornwall when he was flashed by the camera at 11.15pm on October 27, 2005.

He appealed against his fine, initially citing the 30mph sign was illegal because it had the wrong coloured backboard.

But during the hearing at Dorchester Crown Court Recorder Arnold, sitting with two magistrates, uncovered the mistake.

Kenneth Rogers, representing Mr Dawe, said: "It became apparent during the case that Seatown Road did not exist and therefore the prosecution could not prove its case.

"They couldn't prove it was a restricted road and that means that all convictions on the stretch of road must be doubtful."

It is understood the camera catches an average of 100 drivers a week, meaning that around 3.1 million pounds in fines may have been handed out since 1997 and 156,000 penalty points awarded.

Recorder Arnold said: "The fundamental issue is whether the road upon which Mr Dawe was driving was in fact a restricted road.

"The evidence is that Seatown Road is not the name of a road in Chideock. We cannot be sure that the stretch of road is a restricted road."

Paul Smith, from the road safety group Safe Speed, said: "If these convictions are incorrect then they are fraudulent and everybody must be compensated.

"There are probably people who have lost their jobs because of it and they should get compensation."

Pat Garrett, head of the Dorset Safety Camera Partnership, refused to comment on the matter as the CPS was still considering the ruling.